Electrical energy may be stored in various forms, such as batteries that undergo a chemical reaction, capacitors that build an electric charge field, and electrical machine driven flywheels that store the electrical energy as kinetic energy. Electrical machines may be particularly suitable for large loads due to the relatively large levels of kinetic energy that may be stored in the rotating flywheels. In particular, electrical machines have been developed as variable speed drives for such loads as servo motors and propulsion motors that typically expend large amounts of energy in a relatively short period of time.
Electrical machines often adversely affect the power factor of the electrical source from which they are driven. Additionally, these electrical machines may generate relatively strong transient voltages that may be injected back into the source when short bursts of energy from the electrical machine are consumed. To alleviate this problem, the electrical machine can be configured with multiple ports for which one or more ports are used for real power bidirectional flow or energy storage and at least one port is used as a source or sink of reactive power that can correct for input power factor, to provide additional filtering of the load or to provide additional filtering and voltage regulation of the source.